Base station device, and mobile station device

ABSTRACT

Provided are a base station device and a mobile station device, which can lighten a cell-search processing. The base station device ( 100 ) includes a frame constitution unit ( 130 ) for forming a frame, in which a pilot symbol multiplied by a base station scrambling code assigned to that device and a plurality of sequences contained in the corresponding sequence set is arranged in at least the head or tail, and a radio transmission unit ( 155 ) for sending the formed frame. On the receiving side of the frame, the frame timing can be detected from the position of a pilot symbol contained in that frame. Since the base station scrambling code and the sequence set containing the sequences are made to correspond to each other, candidates can be narrowed to at most the base station scrambling codes of the number of the combinations of the sequences contained in the sequence set, by detecting the sequences multiplied by the pilot symbol, so that the cell search processing can be lightened.

TECHNICAL FIELD

The present invention relates to a base station apparatus and a mobilestation apparatus that performs a cell search based on a signal fromthat base station apparatus.

BACKGROUND ART

When powered on or during handover, a mobile station such as a mobilephone can communicate by appropriately selecting and using a cell (basestation). Selection of a cell by a mobile station is called a cellsearch. In a cell search, a mobile station selects the optimal cell tobe connected to when powered on. Specifically, each cell is identifiedby a unique scrambling code, and a cell search is performed by a mobilestation detecting the scrambling code of the cell that transmits thesignal with the greatest received power in a downlink.

A conventional technology related to this is a three-step initial cellsearch method in OFCDM (Orthogonal Frequency and Code DivisionMultiplexing) (see Patent Document 1, for example).

With the conventional technology described in Patent Document 1,scrambling codes can be fast detected by grouping scrambling codes intoa number of groups. Specifically, in the first step, symbol timing isdetected by means of guard interval correlation; in the second step,frame timing and a code group are simultaneously detected by calculatingcorrelations between temporally adjacent OFDM symbols; and in the thirdstep, a scrambling code is identified by means of correlationcalculation from between pilot symbol and scrambling code candidatesbelonging to the code group detected in the second step.

FIG. 1 shows a conventional OFCDM frame configuration. As shown in FIG.1, there are consecutive pilot symbols in the time domain at a frameboundary, and a code group sequence indicating a scrambling code groupis multiplied by a frame-end pilot symbol.

FIG. 2 shows conventional second-step processing of a cell searchperformed by a mobile station. The mobile station performs frame timingand scrambling code group detection by calculating correlations betweena sequence extracted by differential demodulation between adjacentsymbols and a code group sequence of all code group candidates. A codegroup and frame timing are detected simultaneously by detecting the codegroup and timing for which the maximum correlation value between theseadjacent pilot symbols is calculated.

-   Patent Document 1: Unexamined Japanese Patent Publication No.    2003-244763

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, a problem with the conventional technology is that, since ascrambling code group is identified using all code group candidates inthe second step, and a scrambling code is identified in the third stepby calculating correlations using all scrambling code candidatesbelonging to the identified scrambling code group, there is an increasedamount of calculation until scrambling code identification.

It is an object of the present invention to provide a base stationapparatus and mobile station apparatus that enable cell searchprocessing to be alleviated.

Means for Solving the Problems

A base station apparatus of the present invention employs aconfiguration that includes: a frame forming section that forms a frameby arranging a pilot symbol multiplied by a plurality of sequencescontained in a sequence set corresponding to a code group to which abase station scrambling code assigned to that apparatus belongs at leastthe start or end; and a transmitting section that transmits the formedframe.

A mobile station apparatus of the present invention employs aconfiguration that includes: a receiving section that receives a framein which a pilot symbol multiplied by a plurality of sequences containedin a sequence set corresponding to a code group to which a base stationscrambling code belongs is arranged at least the start or end; acorrespondence table in which the base station scrambling code and thesequence set are mutually associated; a correlation section thatmultiplies all the sequence candidates by the frame and calculatescorrelations; a sequence set detection section that defects frame timingand a plurality of sequences multiplied by the pilot symbol based oncorrelation values calculated by the correlation section; and a basestation scrambling code detection section that identifies scramblingcode candidates corresponding to the sequence set containing thedetected sequences, and detects the base station scrambling code fromamong the scrambling code candidates.

Advantageous Effect of the Invention

According to the present invention, a base station apparatus and mobilestation apparatus can be provided that enable cell search processing tobe alleviated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing the transmission frame structure of aconventional base station apparatus;

FIG. 2 is a drawing showing a cell search operation of a conventionalmobile station apparatus;

FIG. 3 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 4 is a drawing showing a sample configuration of a correspondencetable of Embodiment 1;

FIG. 5 is a drawing explaining a frame configuration of Embodiment 1;

FIG. 6 is a block diagram showing the configuration of a mobile stationapparatus according to Embodiment 1;

FIG. 7 is a drawing explaining the operation of the adjacent symbolcorrelation section and code group sequence correlation section in FIG.6;

FIG. 8 is a flowchart explaining the operation of the mobile stationapparatus in FIG. 6;

FIG. 9 is a block diagram showing the configuration of a mobile stationapparatus according to Embodiment 2;

FIG. 10 is a flowchart explaining the operation of the mobile stationapparatus in FIG. 9;

FIG. 11 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 3;

FIG. 12 is a drawing explaining a frame configuration of Embodiment 3;

FIG. 13 is a block diagram showing the configuration of a mobile stationapparatus according to Embodiment 3;

FIG. 14 is a flowchart explaining the operation of the mobile stationapparatus in FIG. 13;

FIG. 15 is a block diagram showing the configuration of a mobile stationapparatus according to Embodiment 4;

FIG. 16 is a block diagram showing the configuration of a mobile stationapparatus according to Embodiment 5;

FIG. 17 is a drawing showing a sample configuration of a correspondencetable of Embodiment 5;

FIG. 18 is a flowchart explaining the operation of the mobile stationapparatus in FIG. 16; and

FIG. 19 is a block diagram showing the configuration of a mobile stationapparatus according to Embodiment 6.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. In the embodiments,identical components are assigned the same reference numerals, andduplicate descriptions thereof are omitted.

Embodiment 1

As shown in FIG. 3, a base station apparatus 100 of Embodiment 1 has acoding section 105, a modulation section 110, a pilot signal generationsection 115, a code group sequence generation section 120, a code groupsequence multiplication section 125, a frame configuration section 130,a scrambling code generation section 135, a scrambling section 140, anIFFT section 145, a GI insertion section 150, a radio transmissionsection 155, a radio reception section 160, a GI removal section 165, anFFT section 170, a demodulation section 175, and a decoding section 180.

Coding section 105 has a transmit signal (DCH or the like) as input,performs predetermined coding, and outputs a coded signal to modulationsection 110.

Modulation section 110 has the coded signal from coding section 105 asinput, performs predetermined primary modulation (generally, primarymodulation according to the transmit signal QoS or radio channel state)in subcarrier units, and outputs a modulated signal to frameconfiguration section 130.

Pilot signal generation section 115 generates a pilot signal (CPICH)common to all cells, and outputs the generated pilot signal to codegroup sequence multiplication section 125.

Code group sequence generation section 120 has a scrambling code numberas input from scrambling code generation section 135. Then code groupsequence generation section 120 references a scrambling code number/codegroup sequence set correspondence table (see FIG. 4), and selects a codegroup sequence set to be multiplied by a frame-end pilot (CPICH). Codegroup sequence generation section 120 then outputs the selectedscrambling code group sequence set to code group sequence multiplicationsection 125. Here, the correspondence a table shown in FIG. 4 indicatesthe correspondence between a scrambling code unique to each base stationapparatus 100 and a code group sequence set assigned to that scramblingcode. This code group sequence set is composed of a plurality of codegroup sequences (which may be of one type). Code group sequences used inthis embodiment are mutually-orthogonal orthogonal sequences. Here, codegroup sequences in a conventional system are used, but this is not alimitation, and any orthogonal sequences that are mutually orthogonalmay be used. However, using orthogonal sequences already provided in aconventional system obviates the necessity of preparing orthogonalsequences for a system of this embodiment, enabling the systemconstruction workload to be alleviated.

Code group sequence multiplication section 125 has a code group sequenceset from code group sequence generation section 120 as input. Then codegroup sequence multiplication section 125 multiplies the pilot signalfrom pilot signal generation section 115 by all the code group sequencescomposing the code group sequence set. Code group sequencemultiplication section 125 then outputs two sequences—the pilot signalitself, and a sequence in which the pilot signal has been multiplied bythe code group sequences—to frame configuration section 130.

Frame configuration section 130 has a modulated signal as input frommodulation section 110, and also has a pilot signal and a pilot signalmultiplied by code group sequences as input from code group sequencemultiplication section 125. Then frame configuration section 130 forms aframe having a configuration in which a pilot signal is arranged at thestart, and a pilot signal multiplied by code group sequences at the end,and a modulated signal (data) is arranged in the remainder (see FIG. 5).Frame configuration section 130 then outputs an OFDM symbol with an OFDMsymbol that is subcarrier number N symbols as a unit.

Scrambling code generation section 135 generates a scrambling codeaccording to the scrambling code number unique to base station apparatus100. Then scrambling code generation section 135 outputs the scramblingcode number to code group sequence generation section 120, and alsooutputs the generated scrambling code to scrambling section 140.

Scrambling section 140 has a scrambling code as input from scramblingcode generation section 135 and also has transmit data as input fromframe configuration section 130 in OFDM symbol units, and performsscrambling by multiplying each OFDM symbol by the scrambling code. Thescrambled transmission data is output to IFFT section 145.

IFFT section 145 has the scrambled transmission data as input fromscrambling section 140, generates a multicarrier signal by convertingthe frequency-domain signal to a time-domain signal, and outputs themulticarrier signal to GI (Guard Interval) insertion section 150.

GI insertion section 150 inserts a guard interval for each OFDM symbol,and outputs a signal to which the guard interval is inserted, to radiotransmission section 155.

Radio transmission section 155 has the signal to which the guardinterval is inserted, as input from GI insertion section 150, performsRF processing such as up-conversion, and transmits the resulting signalvia an antenna.

Radio reception section 110 receives a signal from a mobile stationapparatus via the antenna, performs RF processing such asdown-conversion, and outputs a signal that has undergone RF processingto GI removal section 165.

GI removal section 165 has the signal that has undergone RF processingas input from radio reception section 160, removes the guard interval,and outputs the resulting signal to FFT section 170.

FFT section 170 has the received OFDM signal that has undergone guardinterval removal as input from radio reception section 160, converts thetime-domain signal to a frequency-domain signal, and extracts subcarriersignals from the multicarrier signal. Then a signal that has undergoneFFT processing is output to demodulation section 175.

Demodulation section 175 has the signal that has undergone FFTprocessing as input from FFT section 170, and performs demodulation on asubcarrier-by-subcarrier basis. After subcarrier demodulation, thesignal is output to decoding section 180.

Decoding section 180 has the demodulated signal as input fromdemodulation section 175, performs appropriate error correctiondecoding, and extracts a received signal.

As shown in FIG. 6, a mobile station apparatus 200 of Embodiment 1 has areception control section 205, a radio reception section 210, a symboltiming detection section 215, a GI removal section 220, an FFTprocessing section 225, an adjacent symbol correlation section 230, acode group sequence replica generation section 235, a code groupsequence correlation section 240, a frame timing/code group detectionsection 245, a scrambling code identification section 250, a scramblingcode replica generation section 255, a descrambling section 260, adecoding section 265, a CRC check section 270, a coding section 275, amodulation section 280, a GI insertion section 285, and a radiotransmission section 290.

Reception control section 205 performs control relating to the outputdestination of an output signal from radio reception section 210according to the state of mobile station apparatus 200—that is,according to which step of the initial cell search mode is in effect, orwhether normal receive mode is in effect—or the success or failure ofcode identification. Specifically, reception control section 205controls the output destination of an output signal from radio receptionsection 210 by outputting an output destination directive signal toradio reception section 210. This output destination directive signalindicates that symbol timing detection section 215 is the outputdestination when the state of mobile station apparatus 200 is the firststep of the initial cell search mode, or indicates that GI removalsection 220 is the output destination when the state of mobile stationapparatus 200 is other than the first step.

Radio reception section 210 receives a signal from base stationapparatus 100 via an antenna, and performs RF processing such asdown-conversion. Then radio reception section 210 outputs a signal thathas undergone RF processing to the output destination indicated by theabove-described output destination directive signal from receptioncontrol section 205.

Symbol timing detection section 215 has as input a signal that hasundergone RF processing from radio reception section 210 when the mobilestation apparatus is in the initial cell search mode. Symbol timingdetection section 215 calculates guard interval correlation and detectsOFDM symbol timing using the correlation characteristic of guardintervals in OFDM symbols. That is to say, this OFDM symbol timing isFFT window timing for implementing FFT. While guard interval correlationis executed in symbol units, the accuracy or symbol timing detection canbe increased by averaging correlation values over one frame. Then symboltiming detection section 215 outputs the detected symbol timing resultto GI removal section 220, and also outputs to reception control section205 a first step end report signal reporting that symbol timing has beendetected—that is, the first step of the cell search has ended.

GI removal section 220 removes guard intervals from a received signalthat has undergone RF processing in accordance with the OFDM symboltiming from symbol timing detection section 215, and outputs the signalto FFT processing section 225.

FFT processing section 225 has a received signal that has undergoneguard interval removal from GI removal section 220 as input in OFDMsymbol units, and executes FFT processing on this input signal. Then FETprocessing section 225 outputs a signal that has undergone FFTprocessing to an output destination in accordance with the outputdestination directive signal from reception control section 205.Specifically, when the current state of mobile station apparatus 200 isthe second step of a cell search, FFT processing section 225 has asinput an output destination directive signal indicating that adjacentsymbol correlation section 230 is the output destination, and outputs asignal that has undergone FFT processing to adjacent symbol correlationsection 230. On the other hand, when the current state of mobile stationapparatus 200 is the third step of a cell search, FFT processing section225 has as input an output destination directive signal indicating thatscrambling code identification section 250 is the output destination,and outputs an OFDM symbol containing a pilot signal that has undergoneFFT processing and that is arranged at the start of a frame toscrambling code identification section 250. Only a scrambling code ismultiplied by this OFDM symbol containing a pilot signal arranged at thestart of a frame, and any code group sequences is not multiplied.Alternatively, when an output destination directive signal other than anoutput destination directive signal indicating that adjacent symbolcorrelation section 230 is the output destination or an outputdestination directive signal indicating that scrambling codeidentification section 250 is the output destination is input fromreception control section 205, FFT processing section 225 outputs asignal that has undergone FFT processing to descrambling section 260.

Adjacent symbol correlation section 230 has a signal that has undergoneFFT processing as input from FFT processing section 225, and calculatesa correlation sequence with correlation calculated between twotemporally consecutive OFDM symbols (see FIG. 7). This correlationsequence calculation is performed over n frames in order to subsequentlyaverage correlation values between correlation sequence and code groupsequence replica. A calculated correlation sequence is then output tocode group sequence correlation section 240.

Code group sequence replica generation section 235 generates all thecode group sequences calculated beforehand in the system, and outputsthese to code group sequence correlation section 240

As shown in FIG. 7, code group sequence correlation section 240 has acorrelation sequence calculated by adjacent symbol correlation section230 and code group sequences from code group sequence replica generationsection 235 as input, and calculates correlations between thecorrelation sequence and all the code group sequences. This correlationcomputation is performed for n frames, and an average is calculated forn correlation values calculated from a correlation sequence and codegroup sequences calculated from OFDM symbols having the same temporalposition in the frames. Then code group sequence correlation section 240outputs all the averaged correlation values to frame timing/code groupdetection section 245.

Frame timing/code group detection section 245 has averaged correlationvalues as input from code group sequence correlation section 240, anddetects the maximum correlation value giving the largest value amongthese. Then frame timing/code group detection section 245 stores thetiming in the frame at which the maximum correlation value is calculatedand the code group sequence used in multiplication when that maximumcorrelation value is calculated.

Then frame timing/code group detection section 245 calculates athreshold value used to detect other code group sequences of a codegroup sequence set by means of a predetermined method from the value ofthe maximum correlation value. Specifically, for example, a valuecalculated by subtracting a predetermined value X [dB] from the value ofthe maximum correlation value is used as the above-mentioned thresholdvalue. Then, using the calculated threshold value, frame timing/codegroup detection section 245 detects the largest correlation value fromamong correlation values exceeding this threshold value among theremaining correlation values. Then the timing in the frame correspondingto the correlation value—excluding the above-mentioned stored maximumcorrelation value—having the largest value and having a value exceedingthe threshold value, and the code group sequence used in multiplicationwhen this correlation value is calculated, are stored. If there is nocorrelation value exceeding the threshold value other than the maximumcorrelation value, the code group sequence set multiplied in basestation apparatus 100 that transmits a frame includes code groupsequence of one type. In this case, frame timing/code group detectionsection 245 outputs the timing in the frame at which the previouslystored maximum correlation value is calculated to reception controlsection 205, and outputs the code group sequences corresponding to themaximum correlation value to scrambling code identification section 250.

If there is a correlation value exceeding the threshold value other thanthe maximum correlation value, frame timing/code group detection section245 determines whether or not the timing in the frame corresponding tothe correlation value—excluding the above-mentioned stored maximumcorrelation value—having the largest value and having a value exceedingthe threshold value, and the timing in the frame at which the maximumcorrelation value is calculated, coincide. That is to say, frametiming/code group detection section 245 determines whether or nottimings corresponding to two large correlation values coincide. In thisembodiment, a code group sequence set is assumed to be composed of twocode group sequences, and therefore timing in a frame and code groupsequences corresponding to these correlation values are detected asdescribed above for two large correlation values. However, the number ofcode group sequences composing a code group sequence set is not limitedto two, and may be greater than two. In this case, the number ofcorrelation values detected should be increased according to the numberof code group sequences.

If the result of the determination is that the timings corresponding tothe above two correlation values do not coincide, frame timing/codegroup detection section 245 determines that the second step of the cellsearch has failed, and outputs a second step failure indicator that thesecond step has failed to reception control section 205. The reason fordetermining that the second step of the cell search has failed if thetimings corresponding to the above two correlation values do notcoincide is that, since a pilot signal arranged in a frame-end OFDMsymbol is multiplied by a code group sequence set in base stationapparatus 100, it is necessary for the timings corresponding to theabove two correlation values to coincide in order for the successfulsecond step of the cell search.

On the other hand, if the result of the determination is that thetimings corresponding to the above two correlation values coincide,frame timing/code group detection section 245 determines thatsecond-step frame timing detection has succeeded, outputs the detectedframe timing to reception control section 205, and also outputs codegroup sequence identification information (for example, a code groupsequences number) identifying the code group sequences corresponding tothe detected two correlation values to scrambling code identificationsection 250. In this embodiment, scrambling code candidates have alreadybeen narrowed down to two in the step leading to the third step, and theamount of processing is reduced compared with a conventional cell searchmethod in which scrambling codes are only narrowed down to 16corresponding to scrambling codes identified in the second step in thestep leading to the third step.

Scrambling code identification section 250 identifies a scrambling codecorresponding to the code group sequence identification information fromframe timing/code group detection section 245.

Specifically, if code group sequence identification information fromframe timing/code group detection section 245 is of only one type, ascrambling code corresponding to this code group sequencesidentification information can be uniquely identified, and thereforeidentification information for the identified scrambling code is outputto scrambling code replica generation section 255, and a scrambling codereplica generated accordingly is output to descrambling section 260.

On the other hand, if code group sequence identification informationfrom frame timing/code group detection section 245 is of two types,there are two scrambling code candidates identified from a combinationof these code group sequences. Thus, identification information forthese two scrambling code candidates is output to scrambling codereplica generation section 255, and scrambling code replicas generatedaccordingly are received. Then scrambling code identification section250 calculates correlations by multiplying the respective scramblingcode replicas received from scrambling code replica generation section255 by an OFDM symbol containing a pilot signal located at the start ofa frame received from FFT processing section 225. Then the scramblingcode replica for which the largest value is calculated among thecalculated correlation values is identified as the scrambling code, andthe identified scrambling code is output to descrambling section 260.

There are various methods of performing scrambling code identificationin scrambling code identification section 250. For example, it is alsopossible to receive OFDM symbols containing a pilot signal located atthe start of a frame, over n frames from FFT processing section 225,calculate correlations by multiplying these n pilot signals by ascrambling code replica received from scrambling code replica generationsection 255, perform averaging for each correlation result, and identifythe scrambling code replica for which the largest averaged correlationvalue is calculated as the scrambling code.

Scrambling code replica generation section 255 generates scramblingcodes corresponding to scrambling code identification information fromscrambling code identification section 250, and outputs them toscrambling code identification section 250 as a scrambling codereplicas.

Descrambling section 260 has a signal that has undergone FFT processingfrom FFT processing section 225 as input, performs descrambling bymultiplying this signal by the scrambling code received from scramblingcode identification section 250, and outputs the descrambled signal todecoding section 265.

Decoding section 265 has the descrambled signal as input, performsappropriate error correction decoding, and outputs the error correctiondecoding result to CRC check section 270.

CRC check section 270 performs a CRC error check on the error correctiondecoding result from decoding section 265, and if there is no error,determines that the initial cell search has been completed. On the otherhand, if there is an error, CRC check section 270 outputs the CRC errorcheck result to reception control section 205, which should redo theinitial cell search from the first step. On receiving this CRC errorcheck result output when an error is present, reception control section205 outputs an output destination directive signal to radio receptionsection 210 indicating that symbol timing detection section 215 is theoutput destination.

Coding section 275 has a transmit signal such as a DCH as input,executes predetermined coding, an outputs a coded signal to modulationsection 280.

Modulation section 280 has the coded signal as input, performsmodulation according to the transmission signal QoS or radio channelstate, and outputs a modulated signal to radio transmission section 290.

Radio transmission section 290 has the modulated signal as input,performs RF processing such as up-conversion, and transmits theresulting signal via the antenna.

The operation of mobile station apparatus 200 having the above-describedconfiguration will now be explained with reference to FIG. 8

In step ST1001, symbol timing detection section 215 of mobile stationapparatus 200 calculates the guard interval correlation, and detects theOFDM symbol timing using the correlation characteristics of OFDM guardinterval in individual OFDM symbol. This is the first step of theinitial cell search.

In step ST1002 of the second step of the initial cell search, adjacentsymbol correlation section 230 has a signal that has undergone FFTprocessing as input from FFT processing section 225, and calculates acorrelation sequence with correlation calculated between two temporallyconsecutive OFDM symbols. Correlation sequence calculation is performedat all symbol timings in a frame.

In step ST1003, code group sequence correlation section 240 has acorrelation sequence calculated by adjacent symbol correlation section230 and code group sequences from code group sequence replica generationsection 235 as input, and calculates correlations between thecorrelation sequence and all the code group sequences. This correlationcomputation is performed for all symbol timings of n frames.

In step ST1004, code group sequence correlation section 240 performsaveraging for n correlation values calculated between a correlationsequence calculated from OFDM symbols at the same temporal position in aframe and all code group sequences. That is to say, averaging isperformed in frame units, and therefore an averaged correlation valuefor the number of OFDM symbols in one frame is calculated.

In step ST1005, frame timing/code group detection section 245 hasaveraged correlation values as input from code group sequencecorrelation section 240, and detects the maximum correlation value amongthem. Then frame timing/code group detection section 245 stores thesymbol timing at which the maximum correlation value is calculated andthe code group sequence used in multiplication when that maximumcorrelation value is calculated.

The reason for storing the symbol timing at which the maximumcorrelation value is calculated and the code group sequence used inmultiplication when that maximum correlation value is calculated is thatthis symbol timing position is a frame timing candidate, and this codegroup sequence is a key for identifying the scrambling code group. Asthere is no correlation between a pilot signal and transmit data, thecorrelation value between an OFDM symbol containing a pilot signal andan OFDM symbol containing transmit data is a small value. On the otherhand, when the correlation is calculated between OFDM symbols containingending and starting pilot symbols, and when the correlation iscalculated between a code group sequence multiplied by an ending pilotsignal and that code group sequence, a large peak appears. Therefore,OFDM symbol timing at which the correlation value between adjacent OFDMsymbol correlation and a code group sequence is greatest has a highpossibility of being frame timing. Also, a code group sequence givingthe maximum correlation value has a high possibility of being a codegroup sequence multiplied by a pilot signal arranged at the end of aframe in base station apparatus 100 to be accessed.

In step ST1006, frame timing/code group detection section 245 calculatesand sets a threshold value used to detect another code group sequence ofa code group sequence set by means of a predetermined method from thevalue of the maximum correlation value. Specifically, for example, avalue calculated by subtracting a predetermined value X [dB] from themaximum correlation value is used as the above-mentioned thresholdvalue.

In step ST1007, frame timing/code group detection section 245 comparesthe threshold value calculated in step ST1006 with above-describedaveraged correlation values other than the above-described maximumcorrelation value.

If the result of this comparison is that there sa correlation valueexceeding the threshold value other than the maximum correlation value(step ST1007: YES) that correlation value is detected (step ST1008).

In step ST1009, frame timing/code group detection section 245 stores thesymbol timing of the correlation value detected in step ST1008, and thecode group sequence used when calculating that correlation value.

In step ST1010, frame timing/code group detection section 245 comparesthe symbol timings (in other words, the symbol positions in a virtualframe) corresponding to the top two correlation values (the twocorrelation values in high-to-low value order) stored in step ST1005 andstep ST1009.

If the result of the comparison is that the two timings are not thesame—that is, do not coincide—(step ST1010: NO), frame timing/code groupdetection section 245 determines that initial cell search second-stepframe timing identification has failed, and returns to step ST1001 byoutputting a second step failure indicator that the second step hasfailed to reception control section 205.

On the other hand, if the result of the comparison is that the twotimings coincide (step ST1010: YES), frame timing/code group detectionsection 245 determines that second-step frame timing detection hassucceeded, and the relevant frame timing and code group sequences aredeemed to have been identified (step ST1011). Then frame timing/codegroup detection section 245 outputs code group sequence identificationinformation identifying the identified code group sequences toscrambling code identification section 250.

Thus, the success or failure of frame timing identification can bedetermined based on a comparison of the symbol positions of twocorrelation values, and if frame timing is determined to have failed,subsequent calculation processing can be abandoned at that point, andinitial cell search processing can be retried from the first step. As aresult, a cell search can be redone without delay in the event of afailure, enabling fast cell search.

Also, if the result of the comparison is that there is no correlationvalue exceeding the threshold value other than the maximum correlationvalue (step ST1007: NO), the processing flow proceeds to step ST1011,and frame timing/code group detection section 245 identifies the itemsstored in step ST1005 as the frame timing and code group sequence. Thenframe timing/code group detection section 245 outputs code groupsequence identification information identifying the identified codegroup sequence to scrambling code identification section 250.

Next, the processing flow proceeds to the third step of the initial cellsearch, and in step ST1012 scrambling code candidates corresponding tothe code group sequence identification information from frametiming/code group detection section 245 are identified. Replicas ofthese candidate scrambling codes are generated sequentially, thecorrelation between a pilot signal and scrambling code replicas in areceived signal of OFDM symbols in which a CPICH is multiplexed iscalculated and a maximum correlation value is detected, and thescrambling code for which the maximum correlation value is calculated isidentified.

Lastly, verification is performed as to whether the identifiedscrambling code is correct, and if it is incorrect, the processing flowreturns to step ST1001. The above-described CRC error check or the like,for example, can be used for this error verification.

In the above description, it is assumed that a transmitted/receivedframe is configured with a pilot signal arranged at the start and apilot signal multiplied by code group sequences arranged at the end, anda modulated signal (data) arranged in the rest of the frame, but framestructure is not limited to this configuration, and a configuration mayalso be used in which, conversely, a pilot signal multiplied by codegroup sequences is arranged at the start and a pilot signal is arrangedat the end. Also, a pilot signal may occupy only one OFDM symbol in aframe, in which case a pilot symbol may be multiplexed in half of thesubcarriers within that one OFDM symbol, and a symbol in which a pilotand code sequences are multiplied may be multiplexed in the other halfof the subcarriers. It is only necessary to detect frame timing byarranging both pilot signals on either side of a frame boundary or byarranging a pilot symbol before or after the frame boundary.

Thus, according to Embodiment 1, a base station apparatus 100 isequipped with: a frame configuration section 130 that forms a frame byarranging a pilot symbol multiplied by a plurality of (code group)sequences contained in a (code group) sequence set corresponding to acode group to which a base station scrambling code assigned to thatapparatus belongs at least the start or end; and a radio transmissionsection 155 that transmits the formed frame.

By this means, a mobile station that receives an above-described framecan detect frame timing from the position of a pilot symbol contained inthat frame, and furthermore candidates are narrowed down to sequencessets of the number of combinations of sequences contained in a sequenceset at the most by detecting a sequence set multiplied by a pilot symboldue to the fact that a base station scrambling code and a (code group)sequence set containing a plurality of (code group) sequences aremutually associated, with the result that third-step scrambling codeidentification processing is alleviated, cell search processing can bealleviated, and a base station scrambling code corresponding to suchsequence set candidates can be fast identified.

Also, according to Embodiment 1, a mobile station apparatus 200 isequipped with: a radio reception section 210 that receives a frame inwhich a pilot symbol multiplied by one or a plurality of (code group)sequences contained in a (code group) sequence set corresponding to acode group to which a base station scrambling code belongs is arrangedat least the start or end; a correspondence table in which the basestation scrambling code and the sequence set are mutually associated; acode group sequence correlation section 240 (adjacent symbol correlationsection 230) serving as a correlation section that multiplies all (codegroup) sequence candidates by the frame and calculates correlations; aframe timing/code group detection section 245 that detects frame timingand one or a plurality of (code group) sequences multiplied by the pilotsymbol based on correlation values calculated by the correlationsection; and a scrambling code identification section 250 thatidentifies scrambling code candidates corresponding to the sequence setcontaining the detected (code group) sequences, and detects the basestation scrambling code from among the scrambling code candidates.

By this means, frame timing can be detected from the posit ion of apilot symbol contained in a received frame, and furthermore candidatesare narrowed down to spreading code sets of the number of combinationsof spreading codes contained in a spreading code set at the most bydetecting a code group sequence set multiplied by a pilot symbol due tothe fact that a base station scrambling code and a sequence setcontaining one or a plurality of (code group) sequences are mutuallyassociated, with the result that cell search processing can bealleviated, and a base station scrambling code corresponding to such aspreading code set candidate can be fast identified.

Adjacent symbol correlation section 230 and code group sequencecorrelation section 240 serving as the above-described correlationsection calculate correlations by sequentially multiplying all the (codegroup) sequence candidates by a correlation sequence between temporallyadjacent symbols in a received frame, and frame timing/code groupdetection section 245 identifies only a number equal to the number of(code group) sequences contained in the (code group) sequence set inhigh-to-low value order from correlation values calculated by thecorrelation section, and detects symbol timing in the (virtual) frame atwhich that identified correlation value is calculated and the (codegroup) sequences used in multiplication when that identified correlationvalue is calculated as the frame timing and the (code group) sequencesmultiplied by the pilot symbol.

By thus calculating correlations by sequentially multiplying all the(code group) sequence candidates by a correlation sequence betweentemporally adjacent symbols in a received frame, and detecting frametiming and a sequence using this correlation value, the effect of phasenoise added to a received frame in the propagation path or the like canbe alleviated, and frame timing and a sequence can be detected moreaccurately.

Embodiment 2

In Embodiment 1, correlation values calculated by calculatingcorrelations for a correlation sequence of adjacent OFDM symbols foreach code group sequence are averaged for each code group sequence overn frames, after which the top one or two correlation values are detectedby means of a threshold value comparison, and the code group sequencesused by a base station is identified by detecting the code groupsequences used in multiplication when the detected correlation value (s)is/are calculated. In contrast, in Embodiment 2, correlation valuescalculated by calculating correlations for a correlation sequence ofadjacent OFDM symbols for each code group sequence are added for eachcode group sequence set, the sum of correlation values are averaged overn/2 frames, and then the code group sequence set by which multiplicationis performed in order to calculate the largest correlation value amongthese averaged correlation values is identified. By this means, thescope of averaging processing is halved compared with the averagingprocessing performed over n frames in Embodiment 1, making a fasterinitial cell search possible. Also, the SN ratio of OFDM receivedsymbols can be increased by performing adding processing, enablingvalues with the same high degree of reliability as in Embodiment 1 to becalculated even though the number of frames for which averagingprocessing is performed is halved, and making it possible to implement ahighly reliable fast initial cell search.

As shown in FIG. 9, a mobile station apparatus 300 of Embodiment 2 has acode group sequence correlation section 310 and a frame timing/codegroup detection section 320.

Code group sequence correlation section 310 has a correlation sequencecalculated by adjacent symbol correlation section 230 and code groupsequences from code group sequence replica generation section 235 asinput, and calculates correlations between the correlation sequence andall the code group sequences. Then code group sequence correlationsection 310 adds correlation values calculated by the above correlationcalculation according to combinations corresponding to code groupsequence sets. Code group sequence correlation section 310 then averagesthe sum of correlation values calculated by this addition for each codegroup sequence set over n/2 frames. Then code group sequence correlationsection 310 outputs all the averaged sum of correlation values to frametiming/code group detection section 320.

Frame timing/code group detection section 320 has averaged sum ofcorrelation values as input from code group sequence correlation section310, and detects the maximum sum of correlation values giving thelargest value among these. Then frame timing/code group detectionsection 320 identifies the symbol timing (position) at which the maximumsum of correlation values is calculated and the code group sequence setused in multiplication when the maximum sum of correlation values iscalculated.

Frame timing/code group detection section 320 then outputs informationidentifying the identified code group sequence set to scrambling codeidentification section 250. The information identifying the code groupsequence set may be, for example, code group sequence identificationinformation identifying code group sequences composing the code groupsequence set, or a scrambling code number corresponding to the codegroup sequence set.

The operation of mobile station apparatus 300 having the above-describedconfiguration will now be explained with reference to FIG. 10.

In step ST1003, code group sequence correlation section 310 has acorrelation sequence calculated by adjacent symbol correlation section230 and code group sequences from code group sequence replica generationsection 235 as input, and calculates correlations between thecorrelation sequence and all the code group sequences.

In step ST2001, code group sequence correlation section 310 addscorrelation values calculated by the above correlation calculation bymeans of combinations corresponding to code group sequence set on asymbol-by-symbol basis.

In step ST2002, code group sequence correlation section 310 averages thesum of correlation values calculated by this addition over n/2 frames ona symbol-by-symbol basis. Then code group sequence correlation section310 outputs all the averaged sum of correlation values to frametiming/code group detection section 320.

In step ST2003, frame timing/code group detection section 320 hasaveraged sum of correlation values as input from code group sequencecorrelation section 310, and detects the maximum sum of correlationvalues giving the largest value among them.

In step ST2004, frame timing/code group detection section 320 identifiesthe symbol timing at which the maximum sum of correlation values iscalculated and the code group sequence set used in multiplication whenthe maximum sum of correlation values is calculated.

Frame timing/code group detection section 320 then outputs informationidentifying the identified code group sequences set to scrambling codeidentification section 250.

Thus, according to Embodiment 2, a mobile station apparatus 300 isequipped with: a radio reception section 210 that receives a frame inwhich a pilot symbol multiplied by a plurality of (code group) sequencescontained in a (code group) sequence set corresponding to a base stationscrambling code is arranged at least the start or end; a correspondencetable in which the base station scrambling code and the (code group)sequence set are mutually associated (see FIG. 4); an adjacent symbolcorrelation section 230 and code group sequence correlation section 310that calculate correlation values by successively multiplying all the(code group) sequence candidates by a correlation sequence betweentemporally adjacent symbols in the frame; a frame timing/code groupdetection section 320 that detects frame timing and (code group)sequences multiplied by the pilot symbol based on the correlationvalues; and a scrambling code identification section 250 that determinesscrambling code candidates corresponding to the (code group) sequenceset containing the detected (code group) sequences from thecorrespondence table, and detects the base station scrambling code fromamong the scrambling code candidates.

By this means, the SN ratio of a received symbol can be increased byperforming correlation value adding processing within one symbol,enabling highly reliable values to be calculated even though the numberof averaged frames is halved when averaging processing is performed overa plurality of frames, and making it possible to implement fast cellsearch.

Embodiment 3

In Embodiment 1, code group sequence multiplication of all code groupsequences composing a code group sequence set is performed for allsubcarriers in a frame-end OFDM symbol in base station apparatus 100. Incontrast, in Embodiment 3, subcarriers in a frame-end OFDM symbol aredivided into a plurality of subcarrier blocks in a base stationapparatus, and multiplication is performed for a plurality of code groupsequences corresponding to a code group sequence set for each of thesesubcarrier blocks.

As shown in FIG. 11, a base station apparatus 400 of Embodiment 3 has acode group sequence multiplication section 410 and a frame configurationsection 420.

Code group sequence multiplication section 410 has a code group sequenceset from code group sequences generation section 120 as input. Then codegroup sequence multiplication section 410 multiplies the pilot signalfrom pilot signal generation section 115 by the code group sequencescomposing the code group sequence set, as a result of which a pilotsignal multiplied by each code group sequence is generated. Code groupsequence multiplication section 410 then outputs a plurality ofsequences including the pilot signal itself and a sequence in which thepilot signal has been multiplied by each code group sequence to frameconfiguration section 420.

Frame configuration section 420 has a modulated signal as input frommodulation section 110, and also has a pilot signal and a pilot signalmultiplied by code group sequences as input from code group sequencemultiplication section 410. Then frame configuration section 420 forms aframe having a configuration in which a pilot signal is arranged at thestart, and a pilot signal multiplied by code group sequences at the end,and a modulated signal (data) is arranged in the remainder (see FIG.12). Furthermore, in a frame formed by this frame configuration section420, subcarriers in an OFDM symbol in which the end pilot signal isarranged are divided into several subcarrier blocks, and code groupsequences including a code group sequence set are multiplied or asubcarrier-block by subcarrier-block basis. Specifically, in FIG. 12,subcarriers are divided into two subcarrier blocks comprising alow-frequency-side subcarrier block 1 and a high-frequency-sidesubcarrier block 2, and, for example, code group sequence CG1 that is acomponent of the code group sequence set corresponding to scramblingcode number C2 is multiplied by subcarrier block 1, and CG2 ismultiplied by subcarrier block 2.

To simplify the description, in FIG. 12 subcarriers are divided into twosubcarrier blocks corresponding to the number of code group sequencescontained in a code group sequence set. However, this is not alimitation, and subcarriers may also be divided into two subcarriergroups. That is to say, subcarriers by which each code group sequence ismultiplied need not be subcarrier blocks that are consecutive in thefrequency domain, but may also be arranged in a skipping fashion. Inthis description, a subcarrier block is one form of subcarrier group.Also, if a code group sequence set corresponds to n code groupsequences, the number of subcarrier groups in FIG. 12 will be n.

Frame configuration section 420 then outputs an OFDM symbol with an OFDMsymbol that is subcarrier number N symbols as a unit.

As shown in FIG. 13, a mobile station apparatus 500 of Embodiment 3 hasan adjacent symbol correlation section 510, a code group sequencecorrelation section 520, and a frame timing/code group detection section530.

Adjacent symbol correlation section 510 has a signal that has undergoneFFT processing as input from FFT processing section 225, and calculatesa correlation sequence with correlation calculated between twotemporally consecutive OFDM symbols. This correlation sequencecalculation is performed over n frames in order to perform subsequentaveraging. A calculated correlation sequence is then output to codegroup sequence correlation section 520.

Code group sequence correlation section 520 has a correlation sequencecalculated by adjacent symbol correlation section 510 and code groupsequences from code group sequence replica generation section 235 asinput, and calculates correlations between the correlation sequence andall the code group sequences. Here, unlike in Embodiment 1, correlationsare calculated on a subcarrier-block by subcarrier-block basis. That isto say, in Embodiment 3 the code group sequence length is half that inEmbodiment 1.

This correlation calculation is performed for n frames, and code groupsequence correlation section 520 calculates an average for n correlationvalues calculated from a correlation sequence and code group sequencescalculated from OFDM symbols having the same temporal position in theframes. Then code group sequence correlation section 520 outputs all thecorrelation values averaged on a subcarrier-block by subcarrier-blockbasis to frame timing/code group detection section 530.

Frame timing/code group detection section 530 has correlation valuesaveraged on a subcarrier-block by subcarrier-block basis as input fromcode group sequence correlation section 520, and detects the maximumcorrelation value giving the largest value for each subcarrier block.Then frame timing/code group detection section 530 stores the symboltiming (in a virtual frame) at which the maximum correlation value iscalculated and the code group sequences used in multiplication when thatmaximum correlation value is calculated.

Also, frame timing/code group detection section 530 determines whetheror not timings (in a frame) at which maximum correlation values detectedon a subcarrier-block by subcarrier-block basis are calculated coincide.

If the result of the determination is that timings in a frame at whichmaximum correlation values detected on a subcarrier-block bysubcarrier-block basis are calculated do not coincide, frame timing/codegroup detection section 530 determines that frame timing detection inthe second step of the initial cell search has failed, and outputs asecond step failure indicator that the second step has failed toreception control section 205.

On the other hand, if the result of the determination is that timings(in a frame) at which maximum correlation values detected on asubcarrier-block by subcarrier-block basis are calculated coincide,frame timing/code group detection section 530 determines thatsecond-step frame timing detection has succeeded, outputs the detectedframe timing to reception control section 205, and also outputs codegroup sequence indicator identifying the detected code group sequencesto scrambling code identification section 250.

The operation of mobile station apparatus 500 having the above-describedconfiguration will now be explained with reference to FIG. 14.

In step ST3001, code group sequence correlation section 520 has acorrelation sequence calculated by adjacent symbol correlation section510 and code group sequences from code group sequence replica generationsection 235 as input, and calculates correlations between thecorrelation sequence and all the code group sequences. Here, thiscorrelation calculation is performed on a subcarrier-block bysubcarrier-block basis.

In step ST3002, code group sequence correlation section 520 performsaveraging for each identical subcarrier block for n correlation valuescalculated between a correlation sequence calculated from OFDM symbolsat the same temporal position in a frame and code group sequences.

In step ST3003, frame timing/code group detection section 530 hascorrelation values averaged on a subcarrier-block by subcarrier-blockbasis as input from code group sequence correlation section 520, anddetects the maximum correlation value for each subcarrier block.

In step ST3004, frame timing/code group detection section 530 determineswhether or not timings at which maximum correlation values detected on asubcarrier-block by subcarrier-block basis are calculated coincide.

If the result of the determination is that timings at which maximumcorrelation values detected on a subcarrier-block by subcarrier-blockbasis are calculated do not coincide (step ST3004: NO), frametiming/code group detection section 530 determines that frame timingdetection in the second step of the initial cell search has failed, andreturns to step ST1001 by outputting a second step failure indicatorthat the second step has failed to reception control section 205.

On the other hand, if the result of the determination is that timings atwhich maximum correlation values detected on a subcarrier-block bysubcarrier-block basis are calculated coincide (step ST3004: YES), frametiming/code group detection section 530 determines that second-stepframe timing detection has succeeded, and the relevant frame timing andcode group sequences are deemed to have been identified (step ST1011.Then frame timing/code group detection section 530 outputs the detectedframe timing to reception control section 205, and also outputs codegroup sequence indicator identifying the detected code group sequencesto scrambling code identification section 250.

In the above description, it has been assumed that there isorthogonality between a scrambling code and code group sequences thatare component of a code group sequence set. However, in this embodiment,code group sequence used in multiplication differs for each subcarrierblock, and therefore orthogonality between code group sequences is notnecessarily essential.

Thus, according to Embodiment 3, a base station apparatus 400 isequipped with: a frame configuration section 420 that forms a frame inwhich a plurality of subcarriers are divided into a plurality of groups,and, for each group, a pilot symbol multiplied, one at a time, by (codegroup) sequences contained in a (code group) sequence set correspondingto a base station scrambling code assigned to that apparatus is arrangedat least the start or end; and a radio transmission section 155 thattransmits the formed frame.

A mobile station that receives an above-described frame can detect frametiming from the position of a pilot symbol contained in that frame, andfurthermore scrambling code candidates are narrowed down to the umber ofcombinations of (code group) sequences contained in a (code group)sequence set at the most by detecting a (code group) sequence multipliedby each subcarrier block of a pilot symbol due to the fact that a basestation scrambling code and a (code group) sequence set containing aplurality of (code group) sequences are mutually associated, with theresult that cell search processing can be alleviated, and a base stationscrambling code corresponding to such a spreading code set candidate canbe fast identified.

Also, according to Embodiment 3, a mobile station apparatus 500 isequipped with: a radio reception section 210 that receives a frame inwhich a plurality of subcarriers are divided into a plurality of groups,and, for each subcarrier group, a pilot symbol multiplied, one at atime, by (code group) sequences contained in a (code group) sequence setcorresponding to a base station scrambling code is arranged at least thestart or end; a correspondence table in which the base stationscrambling code and the (code group) sequence set are mutuallyassociated (see FIG. 4); a code group sequence correlation section 520(adjacent symbol correlation section 510) serving as a correlationsection that calculates a correlation sequence by sequentiallymultiplying all (code group) sequence candidates by each subcarriergroup; a frame timing/code group detection section 530 that detects, foreach subcarrier group, frame timing and the (code group) sequencesmultiplied by the pilot symbol based on a correlation value calculatedby the correlation section; and a scrambling code identification section250 that identifies scrambling code candidates corresponding to acombination of detected (code group) sequences from the correspondencetable, and detects the base station scrambling code from among thescrambling code candidates.

By this means, frame timing can be detected from the position of a pilotsymbol contained in a received frame, and furthermore candidates arenarrowed down to a (code group) sequence set of the number ofcombinations of (code group) sequences contained in a (code group)sequence set at the most by detecting a (code group) sequence multipliedby each subcarrier group of a pilot symbol due to the fact that a basestation scrambling code is associated as a combination of a plurality of(code group) sequences, a base station scrambling code corresponding tosuch a (code group) sequence set candidate can be fast identified, andinitial cell search processing can be alleviated.

Adjacent symbol correlation section 510 and code group sequencecorrelation section 520 serving as the above-described correlationsection calculate correlations by sequentially multiplying all the (codegroup) sequence candidates by a correlation value between temporallyadjacent symbols in a frame, and frame timing/code group detectionsection 530 detects the maximum correlation value in each subcarriergroup from correlation values calculated by the correlation section, anddetects the timing at which that detected maximum correlation value iscalculated and the code group sequence used in multiplication when thedetected maximum correlation value of each subcarrier group iscalculated as the frame timing and the (code group) sequence multipliedby each subcarrier group of the pilot symbol.

Embodiment 4

In Embodiment 3, correlation is calculated for correlation values ofadjacent OFDM symbols for each code group sequence and the calculatedcorrelation values are averaged over n frames for each code groupsequence and subcarrier-block, after which identification is performedof the code group sequences used in multiplication when the largestcorrelation value is calculated on a subcarrier-block bysubcarrier-block basis. In contrast, in Embodiment 4, correlation valuescalculated by calculating correlations for a correlation sequence ofadjacent OFDM symbols for each code group sequence and subcarrier blockare added for each code group sequence set, the sum of correlationvalues are averaged over n/2 frames, and then the code group sequenceset by which multiplication is performed in order to calculate thelargest correlation value among these averaged correlation values isidentified. By this means, the SN ratio of correlation values within oneOFDM symbol is improved, and therefore the scope of averaging processingperformed over n frames is halved, making a faster cell search possible.Also, since the SN ratio of OFDM received symbols can be increased byperforming adding processing, values with the same high degree ofreliability as in Embodiment 3 can be calculated even though the numberof frames for which averaging processing is performed is halved, and afaster cell search can be implemented.

As shown in FIG. 15, a mobile station apparatus 600 of Embodiment 4 hasa code group sequence correlation section 610 and a frame timing/codegroup detection section 620.

Code group sequence correlation section 610 has a correlation sequencecalculated by adjacent symbol correlation section 510 and code groupsequences from code group sequence replica generation section 235 asinput, and calculates correlations between the correlation sequence andall the code group sequences. Here, correlation sequence calculation andcorrelation between the correlation sequence and all the code groupsequences are performed on a subcarrier-block by subcarrier-block basis.

Then code group sequence correlation section 610 adds correlation valuescalculated by the above correlation calculation by means of combinationscorresponding to code group sequence sets. Code group sequencecorrelation section 610 then averages the sum of correlation valuescalculated by this addition for each code group sequence set over n/2frames. Then code group sequence correlation section 610 outputs all theaveraged sum of correlation values to frame timing/code group detectionsection 620.

Frame timing/code group detection section 620 has averaged sum ofcorrelation values as input from code group sequence correlation section610, and detects the maximum sum of correlation values. Then frametiming/code group detection section 620 identifies the timing at whichthe maximum sum of correlation values is calculated and the code groupsequence set used in multiplication when the maximum sum of correlationvalues is calculated.

Frame timing/code group detection section 620 then outputs informationidentifying the identified code group sequence set to scrambling codeidentification section 250. The information identifying the code groupsequence set may be, for example, code group sequence indicatoridentifying code group sequences composing the code group sequence set,or a scrambling code number corresponding to the code group sequenceset.

In this embodiment, it is basically necessary to identify code groupsequences from a sum of correlation values multiplied by a plurality ofcode group sequences, and it is therefore necessary to maintainorthogonality between code group sequences.

Thus, according to Embodiment 4, a mobile station apparatus 600 isequipped with: a radio reception section 210 that receives a frame inwhich a plurality of subcarriers are divided into a plurality of groups,and, for each subcarrier group, a pilot symbol multiplied, one at atime, by (code group) sequences contained in a (code group) sequence setcorresponding to a base station scrambling code is arranged at least thestart or end; a correspondence table in which the base stationscrambling code and the (code group) sequence set are mutuallyassociated (see FIG. 4); an adjacent symbol correlation section 510 anda code group sequence correlation section 610 serving as a correlationsection that calculates correlations by multiplying all candidates ofthe (code group) sequences by a correlation sequence between temporallyadjacent OFDM symbols in the frame for each subcarrier group andcalculates a sum of correlation values by adding the calculatedcorrelation values according to combinations corresponding to the (codegroup) sequence set; a frame timing/code group detection section 620that specifies a maximum sum of correlation values from the sum ofcorrelation values and detects a timing in the frame at which thespecified maximum sum of correlation values is calculated and the (codegroup) sequences multiplied upon calculating the specified maximum sumof correlation values as the frame timing and the (code group) sequencesmultiplied by the pilot symbol; and a scrambling code identificationsection 250 that determines scrambling code candidates corresponding tothe (code group) sequence set containing the detected (code group)sequences from the correspondence table, and detects the base stationscrambling code from among the scrambling code candidates.

By this means, the SN ratio of received symbols can be increased byperforming correlation value adding processing, enabling values with ahigh degree of reliability to be calculated even though the number offrames for which averaging is performed is halved when averagingprocessing is performed over a plurality of frames, and making itpossible to implement a faster cell search.

Embodiment 5

In Embodiment 3, correlation is calculated for a correlation sequence ofadjacent OFDM symbols for each code group sequence and the calculatedcorrelation values are averaged over n frames for each code groupsequence and subcarrier block, after which identification is performedof the code group sequences used in multiplication when the largestcorrelation value is calculated on a subcarrier-block bysubcarrier-block basis. In contrast, in Embodiment 5, a scrambling codecan also be identified at the point in time at which a per-subcarriercode group sequence is identified by further mutually associatingsubcarrier blocks and code group sequences. That is to say, the thirdstep of a cell search can be omitted.

As shown in FIG. 16, a mobile station apparatus 700 of Embodiment 5 hasa frame timing/code group detection section 710 and a scrambling codeidentification section 720.

Frame timing/code group detection section 710 has correlation valuesaveraged on a subcarrier-block by subcarrier-block basis as input fromcode group sequence correlation section 520 and detects the maximumcorrelation value that gives the largest value for each subcarrierblock. Then frame timing/code group detection section 710 stores thetiming in a frame at which the maximum correlation value is calculatedand the code group sequences used in multiplication when the maximum sumof correlation values is calculated.

Also, frame timing/code group detection section 710 determines whetheror not timings in a frame at which maximum correlation values detectedon a subcarrier-block by subcarrier-block basis are calculated coincide.

If the result of the determination is that timings in a frame at whichmaximum correlation values detected on a subcarrier-block bysubcarrier-block basis are calculated do not coincide, frame timing/codegroup detection section 710 determines that frame timing detection inthe second step of the initial cell search has failed, and outputs asecond step failure indicator that the second step has failed toreception control section 205.

On the other hand, if the result of the determination is that timings ina frame at which maximum correlation values detected on asubcarrier-block by subcarrier-block basis are calculated coincide,frame timing/code group detection section 710 determines thatsecond-step frame timing detection has succeeded, outputs the detectedframe timing to reception control section 205, and also outputs codegroup sequence indicator identifying the detected code group sequences,and indicator as to the subcarrier block in which that code groupsequence is detected, to scrambling code identification section 720 inmutually associated form.

Scrambling code identification section 720 references the table shown inFIG. 17 and identifies a scrambling code corresponding to the code groupsequence indicator and subcarrier block indicator from frame timing/codegroup detection section 710, causes scrambling code replica generationsection 255 to generate the identified scrambling code, and outputs thisto descrambling section 260. In this embodiment, a base stationapparatus multiplies a code group sequence set—that is, code groupsequences stipulated for each subcarrier group—based on the basestation's own scrambling code number in accordance with the table inFIG. 17.

The operation of mobile station apparatus 700 having the above-describedconfiguration will now be explained with reference to FIG. 18.

If timings in a frame at which maximum correlation values detected on asubcarrier-block by subcarrier-block basis are calculated coincide (stepST3004: YES), in step ST4001 frame timing/code group detection section710 determines that second-step frame timing detection has succeeded andidentifies the frame timing, and scrambling code identification section720 references the table and identifies a scrambling code correspondingto the code group sequence indicator and subcarrier block indicator fromframe timing/code group detection section 710.

In the above description, it has been assumed that there isorthogonality between a scrambling code and code group sequences thatare component of a code group sequence set. However, in this embodiment,subcarrier blocks are already orthogonal, and therefore orthogonalitybetween code group sequences is not necessarily essential.

Thus, according to Embodiment 5, a mobile station apparatus 700 isequipped with: a radio reception section 210 that receives a frame inwhich a plurality of subcarriers are divided into a plurality of groups,and, for each subcarrier group, a pilot symbol multiplied, one at atime, by (code group) sequences contained in a (code group) sequence setcorresponding to a base station scrambling code is arranged at least thestart or end; a correspondence table in which the base stationscrambling code, the (code group) sequence set and indicator for thesubcarrier group by which (code group) sequences contained in that (codegroup) sequence set is multiplied are mutually associated (see FIG. 17);a code group sequence correlation section 520 serving as a correlationsection that calculates correlations by sequentially multiplying all(code group) sequences by each subcarrier group; and a frame timing/codegroup detection section 710 and scrambling code identification section720 that detect frame timing and (code group) sequences multiplied bythe pilot symbol based on per-subcarrier-group correlation valuescalculated by the correlation section, and identify the base stationscrambling code using the correspondence table based on the detected(code group) sequences and indicator for the group in which that (codegroup) sequences are detected.

By this means, subcarrier blocks and code group sequences are furthermutually associated as compared with FIG. 4, enabling a scrambling codealso to be identified at the point in time at which a code groupsequence multiplied on a subcarrier-block by subcarrier-block basis isidentified. As a result, the step corresponding to the third step of aconventional cell search can be omitted, enabling initial cell searchprocessing to be alleviated, and a still faster cell search to beimplemented.

Embodiment 6

In Embodiment 5, correlation is calculated for correlation values ofadjacent OFDM symbols for each code group sequence and the calculatedcorrelation values are averaged over n frames for each code groupsequence and subcarrier block, after which identification is performedJO of the code group sequence used in multiplication when the largestcorrelation value is calculated on a subcarrier-block bysubcarrier-block basis. In contrast, in Embodiment 6, correlation valuescalculated by calculating correlations for a correlation sequence ofadjacent OFDM symbols for each code group sequence and subcarrier blockare added for each code group sequence set, taking the correspondencebetween a subcarrier block and code group sequence into consideration,and the sum of correlation values are averaged over n/2 frames, and thenthe code group sequence set by which multiplication is performed inorder to calculate the largest correlation value among these averagedcorrelation values is identified. By this means the SN ratio ofcorrelation values within one OFDM symbol is improved, and therefore thescope of averaging processing performed over n frames is halved, makinga faster cell search possible. Also, since the SN ratio of OFDM receivedsymbols can be increased by performing adding processing, values withthe same high degree of reliability as in Embodiment 5 can be calculatedeven though the number of frames for which averaging processing isperformed is halved, and a faster cell search can be implemented.“Adding for each code group sequence set, taking the correspondencebetween a subcarrier block and code group sequence into consideration”means that, even if the combination of code group sequences contained incode group sequence sets is the same, if the correspondence between codegroup sequences and subcarrier blocks is different, addition isperformed with the code group sequence set treated as different codegroup sequence sets.

As shown in FIG. 19, a mobile station apparatus 800 of Embodiment 6 hasa code group sequence correlation section 810 and a frame timing/codegroup detection section 820.

Code group sequence correlation section 810 has a correlation sequencecalculated by adjacent symbol correlation section 510 and code groupsequences from code group sequence replica generation section 235 asinput, and calculates correlations between the correlation sequence andall the code group sequences. Here, correlation sequence calculation andcorrelation calculation between the correlation sequence and all thecode group sequences are performed on a subcarrier-block bysubcarrier-block basis.

Then code group sequence correlation section 810 adds correlation valuescalculated by the above correlation calculation for each code groupsequence set, taking the correspondence between a subcarrier block andcode group sequence into consideration. Code group sequence correlationsection 810 then averages the sum of correlation values calculated bythis addition for each code group sequence set taking the correspondencebetween a subcarrier block and code group sequence into considerationover n/2 frames. Then code group sequence correlation section 810outputs all the averaged sum of correlation values to frame timing/codegroup detection section 820.

Frame timing/code group detection section 820 has averaged sum ofcorrelation values as input from code group sequence correlation section810, and detects the maximum sum of correlation values. Then frametiming/code group detection section 820 identifies the timing at whichthe maximum sum of correlation values is calculated and the code groupsequence set (taking the correspondence between a subcarrier block andcode group sequences into consideration) used in multiplication when themaximum sum of correlation values is calculated.

Frame timing/code group detection section 820 then outputs code groupsequence indicator identifying the detected code group sequences, andindicator as to the subcarrier block corresponding thereto, toscrambling code identification section 720 in mutually associated form.

In this embodiment, it is basically necessary to identify a code groupsequence from a sum of correlation values multiplied by a plurality ofcode group sequences, and it is therefore necessary to maintainorthogonality between code group sequences.

Thus, according to Embodiment 6, a mobile station apparatus 800 isequipped with: a radio reception section 210 that receives a frame inwhich a plurality of subcarriers are divided into a plurality of groups,and, for each subcarrier group, a pilot symbol multiplied, one at atime, by (code group) sequences contained in a (code group) sequence setcorresponding to a base station scrambling code is arranged at least thestart or end; a correspondence table in which the base stationscrambling code, the (code group) sequence set and indicator for thesubcarrier group by which (code group) sequences contained in that (codegroup) sequence set is multiplied are mutually associated (see FIG. 17);an adjacent symbol correlation section 510 and a code group sequencecorrelation section 810 serving as a correlation section that calculatescorrelations by multiplying all candidates of the (code group) sequenceby a correlation sequence between temporally adjacent OFDM symbols inthe frame for each subcarrier group and calculates a sum of correlationvalues by adding the calculated correlation values for each (code group)sequence set specified by correspondence between the subcarrier groupsand the (code group) sequences corresponding to the (code group)sequence set; a frame timing/code group detection section 820 thatspecifies a maximum sum of correlation values from the sum ofcorrelation values, and identifies a timing in the frame at which theidentified maximum sum of correlation values is calculated and the (codegroup) sequence set for which the identified maximum sum of correlationvalues is calculated; and a scrambling code identification section 720that determines the base station scrambling code corresponding to theidentified (code group) sequence set from the correspondence table.

By this means, the SN ratio of received symbols can be increased byperforming correlation value adding processing, enabling values with ahigh degree of reliability to be calculated even though the number offrames for which averaging is performed is halved when averagingprocessing is performed over a plurality of frames, and making itpossible to implement a faster cell search.

Other Embodiments

In Embodiments 1 through 4, when a base station scrambling code isidentified in the third step of an initial cell search, a pilot symbolby which group code sequences have not been multiplied and only a basestation scrambling code has been multiplied is described as being used.However, the present invention is not limited to this case, and a pilotsymbol by which group code sequences have been multiplied (a pilotsymbol arranged at the start of a frame in each embodiment) can be used.

As a concrete example, a case in which this is applied to Embodiment 1will be described with reference to FIG. 3.

In this case, when the current state of mobile station apparatus 200 isthe third step of a cell search, FFT processing section 225 has as inputan output destination directive signal indicating that scrambling codeidentification section 250 is the output destination, and outputs anOFDM symbol containing a pilot signal that has undergone FFT processingand containing a pilot signal that is arranged at the end of a frame toscrambling code identification section 250.

Scrambling code identification section 250 performs complex conjugatemultiplication of code group sequences identified in the second step,and extracts a pilot signal by which only a scrambling code ismultiplied.

The present application is based on Japanese Patent Application No.2005-198608 filed on Jul. 7, 2005, the entire content of which isexpressly incorporated herein by reference.

INDUSTRIAL APPLICABILITY

A base station apparatus and mobile station apparatus of the presentinvention are useful in enabling cell search processing to bealleviated.

The invention claimed is:
 1. A base station apparatus comprising: aframe forming section that forms a frame, the frame including a firstOFDM symbol and a second OFDM symbol other than the first OFDM symbol,the first OFDM symbol including a first signal generated with firstinformation and a second signal generated with second information, thesecond OFDM symbol including a third signal generated with thirdinformation, the first information and the second information being forsimultaneous use by a mobile station to determine scrambling codecandidates, and the third information being for use by the mobilestation to select a scrambling code from the scrambling code candidates;and a transmitting section that transmits the formed frame.
 2. The basestation apparatus according to claim 1, wherein the frame formingsection allocates the first signal in a first group of subcarriers inthe first OFDM symbol and the second signal in a second group ofsubcarriers in the first OFDM symbol.
 3. A base station apparatuscomprising: a frame forming section that forms a frame, the frameincluding a first OFDM symbol and a second OFDM symbol other than thefirst OFDM symbol, the first OFDM symbol including a first signalgenerated with first information and a second signal generated withsecond information, the second OFDM symbol including a third signalgenerated with third information, the first information and the secondinformation being for use by a mobile station to determine scramblingcode candidates, and the third information being for use by the mobilestation to select a scrambling code from the scrambling code candidates,wherein the scrambling code candidates are directly determined from bothof the first information and the second information; and a transmittingsection that transmits the formed frame.
 4. The base station apparatusaccording to claim 3, wherein the frame forming section allocates thefirst signal in a first group of subcarriers in the first OFDM symboland the second signal in a second group of subcarriers in the first OFDMsymbol.